power: smb1351-charger: improve handling USB insertion/removal

Currently we handle the USB insertion through source detect
interrupt and USB removal through undervolt interrupt.

In certain cases where the VBUS drops less than 5V(say 4.4V)
and VBAT is at 4.3V, PHY disconnects. It will never get
reasserted since the VBUS doesn't drop below 1V and goes back
to 5V.

To handle such corner cases, handle the USB removal for DCP
on the falling edge of UV interrupt and on the falling edge of
SRC_DET interrupt for CDP/SDP.

If we don't enable APSD, still use undervolt interrupt to handle
insertion/removal.

Change-Id: I829ccced5e450c38d6e2dedca20b7f673e19c8b9
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>